LN,
I recently had 3 crates inc. the engine and coming to about 400kg total air-freighted by Bax for less than the figure Fed-ex have quoted you. You may get a quote nearer to what the agents pay by asking for a pre-payed rate.
Another option is to use someone like Big Misters to combine it with one of their container shipments if you can wait an extra few weeks. They are used to dealing with aircraft and parts.